114 J. D. Dana— Volcanic Action. 
this point already in this Journal (xxxi, 396, 1886) and need 
not repeat here. 
15. In external dress the crater of highly viscid lava is very 
unlike that of the feebly viscid. The cone in the former often 
rises with slopes of 30° to 85°; that in the latter, often of but 
5° to 10°. The former commonly uses cinders largely in mak- 
ing its cone, or else has the less fusible Orthoclase Javas to deal 
with ; the latter is chiefly lava-made, cinder-deposits being sub- 
ordinate to those of lava. The crater in one is lengthened up- 
ward at top by cinders; and has cinder cones about each vent 
of liquid lava within the crater; that in the other, is often a 
broad pit, with a floor of cooled lavas over which are large and 
small lava-vents, and low lava-made cones. The volcano of 
the former kind is more liable to catastrophic eruption with 
noisy earth-shocks, though often quiet in some discharges; 
those of the latter commonly work with comparative quiet, 
having their large outflows at times without announcements of 
any kind to those dwelling a few miles away. These are differ- 
ences; but they are differences in some of the results of the 
action going on, not incausesor methods. The first of the two 
kinds of volcanoes prepares for a new eruption by the gradual 
filling of the emptied crater, doing this by means of one or 
more lava-vents in the bottom, which, besides throwing up 
cinders, have their little outflows (as well described by Scacchi 
for Vesuvius), and keep at the work until the crater is filled or 
nearly so; and then comes the break and the greater outflows. 
The second kind differ only as to the cinders; and in Kilauea, 
as to the height of the floor of the crater before the outbreak. 
16. Both from Vesuvius and Kilauea we learn that, next to 
the lava-vent, the crater of a volcanic mountain is its prime or 
most fundamental element. It encloses the extremity of a lava- 
conduit of greater or less breadth that reaches down to the seat 
of fires; and this enclosure exists because of the ejections by 
outflows and upthrows and the consequent down-plunges, which 
superficial conditions in large part determine. The growing 
mountain-cone cannot be rid of its crater except by the gradual 
disappearance and healing over of the lava-vent; and commonly, 
when extinction happens, the crater is still of nearly full size. 
If half or wholly obliterated, it may be again restored ; and is 
likely to be, if action is ever renewed in the region by new 
ascensive action below. If so renewed, it may go forward 
through refusions and new engulfments. But the first step may 
be the opening of the old fissure upon which the crater was 
originally made; in this way the lava conduit might secure for 
itself at once an open way to the surface. 
It may be that the course of the old fissure has been a chief 
cause in determining the form of a crater; and it may lead, in 
